It is known that various types of optical recording media such as CD-R, CD-RW and MO can store a large volume of data. In addition, a randomly accessible medium such as DVD-RAM has recently been developed and widely known as an external memory on information processing equipment such as a computer. For example, a representative example, CD-R, which has a recording layer containing an organic dye, has a laminated structure formed by stacking a dye recording layer and a reflective layer in this order on a transparent disk substrate and further placing a protective layer so as to cover these recording layer and reflective layer. Recording and/or reading are performed by laser light passing through the substrate. Furthermore, to increase the recording capacity of these optical recording media, a multilayered optical recording medium having a plurality of recording layers provided in a single medium has been developed. For example, a dual-layer optical recording medium having two dye recording layers formed on a first transparent disk-form substrate and arranged with an intermediate layer formed of a UV curable resin interposed between them, is reported in Patent Document 1.
It is known that such the dual-layer optical recording medium is formed by the 2P (Photo Polymerization) method using a transparent stamper and by a method comprising forming two disk substrates each having a recording layer and a reflective layer stacked thereon and adhering the two disk substrates with a photocurable resin layer interposed between them. To explain more specifically, the 2P method comprises applying a photocurable resin material onto a first substrate having a first recording layer and a first reflective layer formed thereon, mounting a transparent stamper having irregular forms on the surface coated with the resin, permitting the photocurable resin material to cure, removing the transparent stamper to transfer irregular forms on the surface of the photocurable resin, forming a second recording layer and a second reflective layer sequentially on the irregular surface, and finally adhering a second substrate. Optical information is recorded on and read from the two recording layers by use of recording and/or reading light incident upon the first substrate.
In the method of adhering two disk substrates each having a recording layer and a reflective layer stacked thereon, a dual-layer optical recording medium is manufactured by forming a first disk substrate (hereinafter sometimes referred to as a “conventional-stack structure”) by stacking a recording layer and a reflective layer in this order on a substrate having a guide groove serving as recording truck formed therein, forming a second disk substrate by stacking a reflective layer and a recording layer in this order (hereinafter sometimes referred to as an “inverted-stack structure”) on a substrate, applying a photocurable resin onto each of the disk substrates, combining them such that the resin applied surfaces face each other, and curing the photocurable resin. Optical information is recorded on and read from the two recording layers by use of recording and/or reading light incident on the first substrate. The method of adhering two disk substrates does not require a step of transferring convexes and concaves forms of a transparent stamper, unlike the 2P method. This method is therefore considered excellent in productivity and attaining cost reduction.
Patent Document 1: Japanese Patent Laid-Open No. 2000-311384, Columns [0008] to [0019]